1. Field of the Invention
This invention relates to devices and methods for generating light, and more particularly to electrodeless plasma lamps energized by microwave radiation. Rather than using a waveguide with an air-filled resonant cavity, embodiments of the invention use a waveguide having a body consisting essentially of at least one dielectric material with a dielectric constant greater than approximately 2. Such dielectric materials include solid materials such as ceramics, and liquid materials such as silicone oil. The body is integrated with the waveguide and has at least one lamp chamber containing a bulb.
2. Description of the Related Art
Application Ser. No. 09/809,718 (“ '718”), published as Pub. No. 2002/0011802 A1, disclosed preferred embodiments of a “dielectric waveguide integrated plasma” lamp (DWIPL) including a “dielectric waveguide”, viz, a waveguide having a body consisting essentially of at least one dielectric material with a dielectric constant greater than about 2, and at least one side with at least one lamp chamber (termed a “cavity” therein) extending into the body. A lamp chamber is an open receptacle in a waveguide body having an aperture in a body surface which typically is coplanar with a waveguide surface exposed to the environment. The waveguide is coupled to a source of microwave power by a microwave probe (termed a “feed” therein) positioned within and in intimate contact with the body. The operating frequency and body shape and dimensions are selected such that the waveguide resonates in at least one resonant mode having at least one electric field maximum. Each embodiment disclosed therein has a body consisting essentially of a single solid material, viz., a ceramic, and, with one exception, has a single lamp chamber. A lamp further includes a bulb disposed in each lamp chamber containing a fill mixture (or “fill”) that forms a light-emitting plasma when microwave power is directed by the resonating waveguide body into the bulb. A bulb is either a “bulb envelope,” viz., an enclosure determined by a surrounding wall and a window covering the chamber aperture and hermetically sealed to the wall, or is a self-enclosed discrete bulb within the chamber. The term “bulb cavity,” where used therein, refers to the combination of a lamp chamber and a discrete bulb disposed within the chamber. A bulb cavity need not be hermetically sealed because the fill mixture is confined to the discrete bulb. The waveguide body and bulb(s) are integrated into a unitary structure. The application further disclosed a DWIPL including a dielectric waveguide and a second microwave probe coupled between the waveguide and a source of microwave power. The operating frequency and waveguide body shape and dimensions are selected such that the waveguide resonates in at least one resonant mode having at least one electric field maximum. The lamp further includes feedback means coupled between the second probe and the source, and a bulb disposed within a lamp chamber and containing a fill that forms a light-emitting plasma when microwave power is directed by the resonating waveguide body into the chamber. The waveguide body and chamber are integrated into a unitary structure. The probe connected to the feedback means probes the waveguide to instantaneously sample the field amplitude and phase, and provides this information via the feedback means to the source which dynamically adjusts the operating frequency to maintain at least one resonant mode within the waveguide, thereby operating the lamp in a “dielectric resonant oscillator” mode. The application further disclosed a method for producing light including the steps of: (a) directing microwave power into a waveguide having a body consisting essentially of a solid dielectric material, and an outer surface with a lamp chamber extending into the body, the waveguide resonating in at least one resonant mode having at least one electric field maximum; (b) directing the resonant power into an envelope determined by the chamber and a window, the envelope containing a fill; (c) creating a plasma by interacting the resonant power with the fill, thereby causing light emission; (d) sampling the amplitude and phase of the microwave field within the waveguide; and (e) adjusting the microwave frequency until the sampled power is at a maximum.
The present application is directed to improvements reduced to practice since the '718 application was filed in March 2001. These include advances in design of the (first) “drive probe” which supplies microwave power to the fill, and the (second) “feedback probe”. The probes are connected, respectively, to the output and input of an amplifier to form an oscillator configuration. Additional improvements disclosed herein are utilization of a (third) “start probe” to mitigate over-coupling of the drive probe, and an amplifier and control circuit for three-probe configurations. Also disclosed herein are techniques for sealing a lamp chamber aperture with a window or lens allowing seats to withstand large thermo-mechanical stresses and chamber pressures which develop during lamp operation, and alternative techniques for DWIPL assembly. Also disclosed are waveguide body configurations utilizing two solid dielectric materials, which provide better mechanical and electrical properties than a single solid dielectric material, as well as smaller overall lamp size, better thermal management, lower frequency of operation, and lower cost.